I've always used taps to clean existing bolt holes, I hadn't heard of or seen a thread chaser until I move to Oregon in 2006 If the existing hole is cut properly the tap shouldn't remove any additional material, correct As far as what brand to use I have a set of old Craftman, Vermont and several other brands I've bought over the years. The Vermonts seem to break off easier than any others
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)